NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
211 
lated poster; the small distal canal rarely fuses with the distal zooecia (on which 
consequently the rachis of the mandible is laid). Two or three septulae to the 
zooecial wall. 
Measurements . — Opesium of zooecia 
Opesium of onyehocellarium 
J ho =0.20-0.24 mm. 
Ue>=0.16 mm. 
/? <?ft=0.34-0.36 mm. 
Jon— 0.16 mm. 
Zooecia 
Zs= 0.40 mm. 
lz= 0.30 mm. 
Onychocellaria 
Ton= 0.50 mm. 
lon= 0.24—0.30 mm. 
V aviations . — The important character of this species is the large opesium of 
the onychocellaria which is always longer than the zooecial opesium. This greater 
size is above all very apparent in tangential sections (fig. 12) or in views of the 
interior (fig. 10). At the exterior the breadth of the opesium is reduced in the 
progress of calcification (fig;. 11). but the length always remains quite evident. On 
the same zoarium (fig. 13) one may thus observe both wide and narrow opesia. 
In the underside of the zoarium the zooecia are very irregularly convex; the 
olocyst is covered exteriorly by a thin calcareous pellicle. Finally, it is not rare 
to discover some zoaria incrusting other bryozoa. 
Tangential thin sections (fig. 12) show that the olocyst constitutive of the 
zooecial walls is vacuolar. Such checks in calcification are not rare in old zoaria 
of the Onychocellidae. 
Affinities . — This species differs from Rectonychocella hilamellaria in its un- 
ilamellar zoarium and in its large onychocellarian opesia. 
It differs from Diplopholeos fusi forme in the absence of the zooecial dimor- 
phism, in its unilamellar zoarium, and in its onyehocellarium, which does not fuse 
with the distal zooecium. To differentiate it from this last species is often very 
difficult, and the inexperienced student ought to abstain from any determination 
which does not appear exact to him. 
Occurrence . — Middle Jacksonian: Wilmington. North Carolina (common); 
Baldock, Barnwell County, South Carolina (rare) ; Rich Hill, Crawford County, 
Georgia (common) ; 18 miles west of Wrightsville, Johnson County. Georgia 
(rare) ; 3-1 miles north of Grovania, Georgia (rare) ; Twiggs County, Georgia, one- 
half mile southeast of the Georgia Kaolin Co. Mine (very abundant). 
Upper Jacksonian (Ocala limestone) : Alachua, Florida (common). 
Cotypes. — Cat. No. 63971, U.S.N.M. 
RECTONYCHOCELLA TENUIS, new species. 
Plate 33, tigs. 4-6. 
Description . — The zoarium incrusts shells. The zooecia are elongated, with 
their mural rims confluent. The cryptocyst is very slightly developed, much shorter 
than the opesium, very thin laterally; the opesium is large, elongated, entire, oval, 
or elliptical. The onyehocellarium is larger than the zooecium, fusiform; the distal 
